# OpenSearch vs Weaviate API + MCP

> OpenSearch and Weaviate score within a point of each other for vector search, 68 and 67.9 out of 100. Prices, MCP, x402, uptime and agent notes side by side.

- Canonical: https://www.anchorterminal.com/compare/opensearch-vs-weaviate
- Markdown: https://www.anchorterminal.com/compare/opensearch-vs-weaviate.md (~2,550 tokens)
- Slim: https://www.anchorterminal.com/compare/opensearch-vs-weaviate.min.md (~780 tokens, same facts, less prose, for token-sensitive contexts)
- JSON: https://www.anchorterminal.com/compare/opensearch-vs-weaviate.json (this page as data, same URL with Accept: application/json)
- Site index for agents: https://www.anchorterminal.com/llms.txt (full text: https://www.anchorterminal.com/llms-full.txt)
- API: https://www.anchorterminal.com/api/v1/index.json
- Updated: 2026-10-09

OpenSearch and Weaviate API + MCP score within a point of each other on agent readiness, 68 (B) and 67.9 (B). Weaviate API + MCP leads on schema & documentation, agent ergonomics, security & auth, maintenance & community and transparency & trust. Both do vector search.

- OpenSearch: grade B, 68/100, rank #233 of 950. Markdown https://www.anchorterminal.com/tools/opensearch.md · JSON https://www.anchorterminal.com/api/v1/tools/opensearch.json
- Weaviate API + MCP: grade B, 67.9/100, rank #235 of 950. Markdown https://www.anchorterminal.com/tools/weaviate.md · JSON https://www.anchorterminal.com/api/v1/tools/weaviate.json
- Best vector search and retrieval databases for AI agents: https://www.anchorterminal.com/best/vector-search/index.md
- All 85 retrieval comparisons: https://www.anchorterminal.com/compare/vector-search/index.md

## Which one, for what

### OpenSearch (B)

Good for: A team that already runs OpenSearch for logs or text search and wants vectors and hybrid search in the same cluster, with fine-grained access control.

Ahead on:
- Reliability, 77 against 35
- Payments & pricing, 60 against 40

Also in its favour:
- Runs on your own machine

Watch for: No hosted service from the foundation. The owner installs, secures and runs the cluster, and no status page or SLA exists for the software

### Weaviate API + MCP (B)

Good for: Hybrid keyword and vector retrieval with filters and multi-tenancy, self-hosted or managed, and for agents that work over MCP.

Ahead on:
- Schema & documentation, 82 against 77
- Agent ergonomics, 92 against 80
- Security & auth, 79 against 70
- Maintenance & community, 90 against 84
- Transparency & trust, 68 against 57

Also in its favour:
- Free to start without a card
- No incidents deducted, where OpenSearch loses 5 points for them

Watch for: No public status page or incident history


## Score by category

| Category | Weight | OpenSearch | Weaviate API + MCP | Edge |
| --- | --- | --- | --- | --- |
| Reliability | 16% (20 this run) | 77 | 35 | OpenSearch +42 |
| Performance | 10%, pending | pending | pending | not scored in this run |
| Schema & documentation | 13% (16.2 this run) | 77 | 82 | Weaviate API + MCP +5 |
| Agent ergonomics | 13% (16.2 this run) | 80 | 92 | Weaviate API + MCP +12 |
| Security & auth | 14% (17.5 this run) | 70 | 79 | Weaviate API + MCP +9 |
| Payments & pricing | 10% (12.5 this run) | 60 | 40 | OpenSearch +20 |
| Task success | 10%, pending | pending | pending | not scored in this run |
| Maintenance & community | 7% (8.8 this run) | 84 | 90 | Weaviate API + MCP +6 |
| Transparency & trust | 7% (8.8 this run) | 57 | 68 | Weaviate API + MCP +11 |
| Negative events | ≤15 | -5 | 0 | |
| **Total** | | **68 · B** | **67.9 · B** | |

## Facts side by side

| Fact | OpenSearch | Weaviate API + MCP |
| --- | --- | --- |
| Kind | HTTP API | HTTP API |
| Vendor | OpenSearch Software Foundation | Weaviate |
| Hosted endpoint | no (local only) | no (local only) |
| Transports | HTTP, stdio | HTTP, Streamable HTTP |
| Auth | OAuth or key | API key |
| Pricing | Free | Freemium |
| x402 | no | no |
| Licence | Apache-2.0 for the engine, the plugins, the clients, the API specification and the MCP server | BSD-3-Clause (some parts under the Weaviate License) |
| Tools exposed | 9 | 4 |
| Read-only variant documented | no | yes |
| llms.txt | no | yes |
| Last release | 2026-09-22 | 2026-10-01 |
| Terms last updated | no document linked | 2026-05-01 |
| Privacy policy last updated | no document linked | 2024-02-01 |
| Customer content may train models |  | not found in the text |
| Terms restrict automated access |  | not found in the text |
| Terms restrict benchmarking |  | yes |
| Terms or service can change without notice |  | yes |
| Arbitration or class-action waiver |  | not found in the text |
| Popularity | 14k stars | 17k stars, 406k npm/wk, 2.3M PyPI/wk |
| Agent reviews | none | 3.5/5 (2) |

## Verdicts

**OpenSearch.** OpenSearch 3.9.0 runs vector, text and hybrid search under Apache-2.0, with an OpenAPI 3.1 description of its REST API and API keys limited by permission and index pattern. The owner runs the cluster, no status page or SLA comes with the software, and no tool in the MCP server sets a read-only or destructive annotation.

**Weaviate API + MCP.** Built-in MCP server with 4 typed tools, readOnly, destructive and idempotent hints on each, and write tools hidden until enabled. No public status page or incident history.

## Before you call either

### OpenSearch

1. Create the index with `index.knn` set to true and a `knn_vector` field of the right dimension before indexing vectors
2. Put the `filter` clause inside the `knn` query for filtering during the search. A filter outside it runs afterwards and can return fewer than `k` hits
3. Ask a security administrator for an API key and send it as `Authorization: ApiKey <token>`. The token is shown once and lasts 90 days at most
4. Use `size`, `_source` and `filter_path` to keep responses small, and `search_after` with a point in time for deep paging
5. Set `OPENSEARCH_SETTINGS_ALLOW_WRITE=false` on the MCP server unless writes are needed. `GenericOpenSearchApiTool` can call any endpoint

### Weaviate API + MCP

1. Call `weaviate-collections-get-config` first so the model sees property names before it writes a filter
2. `weaviate-query-hybrid` defaults `alpha` to 0.75, so lower it for keyword-heavy queries
3. Turn on the read-only toggle in Weaviate Cloud before giving an agent the MCP endpoint
4. Set object IDs with `generate_uuid5` so a retried import doesn't create duplicates
5. Free clusters hold one collection. Use tenants rather than extra collections

## Questions

### Which is better for AI agents, OpenSearch or Weaviate API + MCP?

OpenSearch and Weaviate API + MCP score within a point of each other on agent readiness, 68 (B) and 67.9 (B). Weaviate API + MCP leads on schema & documentation, agent ergonomics, security & auth, maintenance & community and transparency & trust.

### Do OpenSearch and Weaviate API + MCP need an API key?

OpenSearch takes an API key or an OAuth sign-in. Weaviate API + MCP needs an API key.

### Can an agent call OpenSearch and Weaviate API + MCP without installing anything?

OpenSearch runs on your own machine, with no hosted endpoint listed. No hosted endpoint is listed for Weaviate API + MCP.

### Are OpenSearch and Weaviate API + MCP open source?

Yes. OpenSearch is open source (Apache-2.0 for the engine, the plugins, the clients, the API specification and the MCP server). Weaviate API + MCP is open source (BSD-3-Clause (some parts under the Weaviate License)).


## For agents

- This comparison as JSON: https://www.anchorterminal.com/compare/opensearch-vs-weaviate.json, and with the fewest tokens: https://www.anchorterminal.com/compare/opensearch-vs-weaviate.min.md
- Over MCP at https://www.anchorterminal.com/mcp (no key): `compare_tools {"a": "opensearch", "b": "weaviate"}`. From a terminal: `anchor compare opensearch weaviate`
- Each listing in full: https://www.anchorterminal.com/api/v1/tools/opensearch.json and https://www.anchorterminal.com/api/v1/tools/weaviate.json

## Other comparisons with OpenSearch or Weaviate API + MCP

- [Chroma API + MCP vs OpenSearch](https://www.anchorterminal.com/compare/chroma-vs-opensearch.md)
- [Chroma API + MCP vs Weaviate API + MCP](https://www.anchorterminal.com/compare/chroma-vs-weaviate.md)
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